Magnesium alloys containing magnesium and various additive elements are lightweight and have high specific strength and specific rigidity and good shock absorbency. Therefore, magnesium alloys have been examined as materials for housings of mobile electric and electronic devices such as cellular phones and laptop computers and materials for parts of automobiles. Since magnesium alloys have a hexagonal crystalline structure (hexagonal close-packed (hcp) structure), they have poor plastic formability at room temperature. Therefore, magnesium alloy structural members are mainly formed of cast materials (e.g., AZ91 alloy of American Society for Testing and Materials (ASTM) standard) by a die casting process or a thixomolding process. However, when a thin sheet, in particular, the above-described structural member is mass-produced, it is difficult to produce a long sheet suitable for such a thin sheet or structural member by the casting process above.
Wrought magnesium alloys such as AZ31 alloy of the ASTM standard are relatively easily subjected to plastic forming. Therefore, it has been examined that the thickness of a cast sheet composed of the wrought magnesium alloy is decreased by subjecting the cast sheet to plastic forming such as rolling or press forming. Patent Literature 1 discloses a sheet including a shear zone left therein by providing bending to a rolled sheet composed of an alloy containing Al in substantially the same amount as that of AZ91 alloy using a roll leveler. This sheet can be continuously recrystallized during press forming and thus has good press formability. Furthermore, since AZ91 alloy and the alloy containing Al in substantially the same amount as that of AZ91 alloy have high corrosion resistance and strength, such an alloy is expected to be increasingly demanded as a wrought material.